ol.overlay.Overlay can be used to bind DOM elements to a
coordinate on the map. It has positioning options to support
e.g. popups or image markers that have an anchor at the bottom
and an unknown size.
The overlayContainer stops propagation on mousedown and
touchstart events, so clicks and gestures on overlays don't
trigger any MapBrowserEvent. To make this work reliably, we now
only fire dblclick in mapbrowserevent.js when there was a
previous mousedown or touchstart. The default container for
controls is now the overlayContainer.
Thanks @fredj for the inspiration. This gives us initial rotation support. It exposes some issues in the interactions that I'll address separately. Closes#22.
When zooming to a new zoom level, we can immediately remove tiles from the previous level. This (strongly) suggests not adding images to the container until they have actually loaded.
We only want to adjust things that have to do with rendering (like the position of the layers panel) when actually rendering. The handleXChange methods may be called more times than we can actually render, so we never want to do anything that touches the DOM there. Instead, we have to keep track of the state at previous render and adjust the layers panel (or other) based on changes only when rendering.
When zooming or panning, if we have tiles at alternate resolutions, those tiles are inserted in the DOM before the tiles at the target resolution. This means you should see blurry tiles instead of whitespace when panning (assuming you've already zoomed in a bit).
Tile pruning code separated into to methods for clarity. Alt-z tiles are only removed when all current-z tiles have loaded. Thanks @elemoine for the excellent debugging session.
